GB2321259A

GB2321259A - Structural members

Info

Publication number: GB2321259A
Application number: GB9701050A
Authority: GB
Inventors: Quinton David St; Malcolm Robert Wallis
Original assignee: WARD BUILDING COMPONENTS LIMIT
Current assignee: WARD BUILDING COMPONENTS LIMIT
Priority date: 1997-01-18
Filing date: 1997-01-18
Publication date: 1998-07-22
Anticipated expiration: 2017-01-18
Also published as: GB9701050D0; GB2354538B; GB2321259B; GB2354467B; GB2354538A; GB2354467A; GB0100195D0; GB0100197D0

Abstract

An elongate structural member comprising an elongate body part of tubular shape of, polygonal cross-section, made of sheet metal which has been cold formed to provide said tubular shape with at least a pair of adjacent edges of the sheet metal being connected together, wherein said pair of adjacent edges are disposed at or adjacent a corner of the tubular shape at which first and second sides, terminating in said adjacent edges, converge to provide a salient angle therebetween and are joined together by a first projecting part (31) of said first side which overlaps said second side and a second projecting part (35) of said second side which overlaps said first side.

Description

Description of the Invention This invention relates to an elongate structural member of tubular shape. Generally the tubular shape is of substantially similar internal and external cross-sectional configuration and such configuration is generally square or rectangular but may be made of any other desired closed polygonal crosssectional configuration, such as rectangular or triangular; moreover, the configuration may be provided with an external shape which has at least one longitudinally extending formation of desired shape, such as at least one groove and/or rib. An elongate structural member of tubular shape of square or rectangular configuration is commonly known as a "box-section structural member".

Such structural members are widely used in buildings and the like as bracing elements, for example, as structural ties for roof structures, trusses, stanchions and space frames. Such structural ties may be provided to accommodate wind loading, in which case they are commonly referred to as wind braces.

Such a structural member has hitherto comprised a hot rolled tube provided with an attachment portion at each end. Such structural members made of hot rolled tube have generally been relatively expensive and heavy. They are made by cutting to length from a stock length of tube of a diameter and wall thickness which approximates as far as possible to that required for the structural strength. However, because the tube is bought in standard sizes, the tube crosssectional dimensions cannot be tailored for each particular application. In addition, the need to cut to length from a standard length generally leads to a significant amount of waste. In addition, the steps of welding on a cap plate to each end of the tube and a T-piece to provide the attachment portions is required to be performed, followed by shotblasting and painting.

Cold formed elongate structural members have been proposed in EP A-0639684 but these proposals have suffered from certain disadvantages relating to the manner of connecting together adjacent edges of the member. In one version the structural member comprises a pair of channel shaped components having, at adjacent edges, inwardly directed lips which are connected together by spot welding or by fastening arrangements which require access to be gained to the interior of the tubular section from one end thereof. In another version, the structural member is made as a one-piece box section element, having, at adjacent edges, out-turned flanges which are connected together by suitable means. The first alternative suffers from the disadvantage of the necessity to gain access to the interior of the cross-section, whilst the second embodiment suffers from the disadvantage of having out-turned flanges which are aesthetically unpleasing and can effect an operational disadvantage.

An object of the present invention is to provide a structural member whereby the above-mentioned disadvantages are overcome or are reduced.

A further object of the invention is to provide a method of making such a structural member.

According to one aspect of the present invention we provide an elongate structural member comprising an elongate body part of tubular shape of, polygonal cross-section, made of sheet metal which has been cold formed to provide said tubular shape with at least a pair of adjacent edges of the sheet metal being connected together, wherein said pair of adjacent edges are disposed at or adjacent a corner of the tubular shape at which first and second sides, terminating in said adjacent edges, converge to provide a salient angle therebetween and are joined together by a first projecting part of said first side which overlaps said second side and a second projecting part of said second side which overlaps said first side.

The elongate body part may be a unitary member longitudinally bounded by said pairs of adjacent edges.

Alternatively, the body part may comprise a compound member, comprising two or more components secured together, each component forming part of the overall cross-section of the body part.

In this case, one edge of said pair of edges is provided on one component, and the other edge of said pair of edges is provided on the other component.

In this alternative there may be at least one further pair of adjacent edges where the sheet metal is connected together and the or each pair of said adjacent edges being disposed at or adjacent a further corner of the tubular shape at which further first and second sides converge to provide a salient angle there between and a further first projecting part of said first further side overlaps said further second side and a further second projecting part of said further second side overlaps said further first side.

Preferably, each first and second projecting part comprises a plurality of first and second projecting elements respectively.

Preferably, each first projecting element is disposed alternately relative to each second projecting element.

Each first and second projecting element may be of generally rectangular configuration comprising a pair of generally parallel sides projecting outwardly from adjacent inner edge parts and terminating in an outer edge part, which is generally perpendicular to each of said sides.

Preferably, said sides, whilst being generally perpendicular to said inner and outer edge parts are inclined thereto to provide a taper whereby the projecting elements decrease in width towards the outer edge part.

Where the corner is a right-angle, each first projecting part may be formed through substantially a right-angle.

The first and second projecting parts may be disposed in a recessed portion of the side which the respective projecting part overlaps so that the external surface of the projecting parts lies substantially in the same plain as the external surface of the main part of the side which it overlaps.

The body part may be provided with an attachment portion at each end.

The body part may have upper and lower sides interconnected by first and second transverse sides extending normally to the respective upper and lower sides over the majority of the length of the body part, the body part having at least adjacent one end a flattened attachment portion so that in this portion the first and second transverse portions of the respective transverse sides are deformed so as to have two parts lying substantially parallel to and between upper and lower portions of the upper and lower sides.

The flattened portions may lie substantially midway between the upper and lower sides.

At least one attachment portion may comprise portions of the elongate member displaced out of their original cross-section positions into positions adjacent to one another and adapted to co-operate with fastening means.

The attachment portion may comprise an upper portion parallel to an upper side of the body part, a lower portion parallel to a lower side of the body part, said upper and lower portions being displaced inwardly relative to their associated upper and lower sides and, disposed therebetween, at opposite sides thereof, first and second transverse portions, each comprising an upper part and a lower part disposed generally in face-to-face relationship with each other and with the respective upper and lower portions and the upper part being connected, at one side, to an outer edge of the upper portion and being connected, at an opposite side, to one edge of the lower part and the lower part being connected at its other edge to an outer edge of the lower portion.

Said first and second transverse portions may be provided as an integral part of the first and second transverse sides of the body portion which are progressively deformed to said face-to-face relationship in a transition region disposed between said body part and said attachment portion.

Alternatively, at least one attachment portion may comprise an attachment component formed separately from said body part and fastened thereto.

The attachment portion may be of channel-shape, the limbs of the channel being disposed in side-by-side relationship with two opposed walls of the body part.

The attachment component may be fastened to said body part by fasteners.

Reinforcing means may be provided to reinforce the walls of the body part.

According to another aspect of the invention we provide a method of providing an elongate structural member comprising a body part of tubular shape, of polygonal cross-section, comprising the steps of cold forming sheet metal to provide said tubular shape and connecting together at least a pair of adjacent edges of the sheet metal and providing a first projecting part of a first side and a second projecting part of a second side of said body part, performing said cold forming step so that said pair of adjacent edges are disposed at or are adjacent a corner of the tubular shape at which said first and second sides converge to provide a salient angle and forming said first projecting part to overlap said second side and said second projecting part to overlap said first side.

Said first and second projecting parts may be provided by a rotary punching unit comprising a pair of rotatable punching elements, one of which is provided with a plurality of recesses and the other of which is provided with a plurality of co-operating projecting punches whereby edge portions of the sheet are punched to provide said projecting portions between parts of the sheet which are punched out by the rotary punching unit.

Alternatively, the first and second projecting parts may be made by a punching operation in a reciprocatory punching unit comprising a first die provided with a plurality of recesses and a second die provided with a plurality of co-operating projecting punches, said dies being reciprocal towards and away from each other so as to provide said projecting parts between portions of the strip which are punched therefrom by said punching unit.

The punching operation may be repeated along the length of the strip.

The first and second projecting parts may be provided before the sheet metal is cold formed to said hollow shape.

The sheet metal may be formed to said hollow shape by roll forming.

The sheet metal may be fed to a pre-punch unit before being provided with the first and second projecting parts, or being roll formed, whereby desired openings may be provided in the sheet metal.

The method may comprise the further step of displacing attachment portions of the member out of their original cross-sectional positions into positions adjacent to one another.

Means may be provided for co-operation of said portions with fastening means.

Where the body part has an upper side and a spaced lower side interconnected by first and second transverse sides perpendicular thereto, means may be provided to displace said first and second transverse sides inwardly, at least at one end, to provide the or each attachment portion, with first and second transverse portions disposed between upper and lower transverse portions, the first and second transverse portions comprising respectively upper and lower transverse parts disposed in face-to-face flattened relationship.

The transverse portions may be initially displaced partially inwardly to an intermediate position to reduce the spacing between said upper and lower portions and subsequently pressure may be supplied to said upper and lower portions to reduce their spacing further and cause the transverse portions that have said upper and lower parts to be brought into face-to-face relationship.

Die means may be provided to define the inclination of the upper and lower sides in an intermediate region between the body part and the attachment portion.

The invention will now be described in more detail by way of example with reference to the accompanying drawings therein: FIGURE 1 is a diagrammatic side elevation of an apparatus for producing a structural member embodying the present invention, FIGURE 2 is a cross-section on the line 2-2 of Figure 1 showing a rotary punching unit, FIGURE 3 is a diagrammatic perspective view of the rotary punching unit of Figure 2, FIGURE 4 is a fragmentary perspective view showing stock material of sheet metal, FIGURE 5 is a diagrammatic perspective view showing the material of Figure 4 after being subjected to a punching operation, FIGURE 6 is a cross-section on the line 6-6 of Figure 1 showing the cross-sectional shape of the metal sheet, FIGURE 7 is a section on the line 7-7 of Figure 1 showing the shape of the metal sheet, FIGURE 8 is a perspective view of a body part of a structural element embodying the invention, FIGURES 9-llb show exploded views of a structural element embodying the invention where the structural element comprises a body part and a separate attachment component providing an attachment portion of the structural member, FIGURE 12 is a perspective view of an elongate structural member embodying the invention where the attachment portion is integral with the body portion, FIGURE 13 is a plan view showing a stage in the production of the attachment portion shown in Figure 12, FIGURE 14 is a side elevation showing a further stage in the method of forming the attachment portion shown in Figure 12, FIGURE 15 is a perspective view showing a stage in the manufacture of the structural member shown in Figure 12.

FIGURE 16 shows a stage in an alternative, reciprocatory punching, manufacturing method and FIGURE 17 is a perspective view, showing an alternative structural member embodying the invention.

Referring to the drawings, as a first step in the manufacture of a structural member, a coil 10 of sheet metal, in the present example, sheet steel, is decoiled in a decoiler 11 and is fed via a loop 12 to a conventional leveller 13 comprising a plurality of alternately disposed rolls so that the sheet metal is alternately bent upwardly and downwardly so as to straighten it. Sheet metal is then fed via a further loop 14 from the leveller 13 to a pair of feed rolls 15 which are driven by a suitable motor, in conventional manner, to feed the strip into a prepunching unit 16 where one or more desired apertures are punched in the strip which, prior to punching, is of the configuration shown in Figure 4. For example, the steel sheet may be prepunched with apertures such as the apertures shown at 17 in Figure 8 or 18 as shown in Figures 12 and 15.

The prepunch unit 16 also cuts the decoiled sheet metal to a desired length. The thus severed sheets are then fed by a blank conveyor 19 to a pair of entry rolls 20, again, of conventional type and driven by a suitable motor so as to pinch the sheet material therebetween and to feed it to a rotary punching unit 21.

Referring now to Figures 2 and 3, the metal sheet is fed between two pairs of rotary punching dies 22, 23. The rotary punching dies 22, 23 are drivably interconnected by meshing gear wheels 24 and are carried on rotatable shafts 25 carrying suitable bearing means, not shown. At least one of the shafts 25 is driven so as to drive the sheet material through the rotary punching unit 21.

The dies 22 have a plurality of projections 26 disposed circumferentially therearound whilst the dies 23 have a plurality of recesses 27 which are adapted to co-operate with the projections 26 so as to punch out material from the metal stock shown in Figure 4 so as to provide, as shown in Figure 5, a first projecting part on one side 31 and a second projecting part 32 on a second side 33 of the sheet material. Each projecting part 30, 32 comprises a plurality of projecting elements 34, 35 respectively. Each projecting element 34, 35 has sides 36 which project from adjacent inner edge portions 38 respectively and are interconnected at their outer ends by an outer edge part 39. The sides 36 are slightly inclined so that the width of the projecting elements decreases towards the outer edge part 39.

As can best be seen from Figure 5, each first projecting element 34 on the first side 31 is longitudinally aligned with a punched out part 34a on the second side 33 and each second projecting element 35 on the second side 33 is longitudinally aligned with a punched out part 35a on the first side 31 so that the projecting elements 34, on the first side 31 are disposed longitudinally alternately relative to the projecting parts 35 on the second side 33.

The sheet material is then fed into a conventional roll former 40 where a plurality of pairs of co-operating rolls form the flat sheet material to a box section as shown in Figure 6 in conventional manner. The slight angle hereinbefore mentioned of the sides 36 of the projecting elements 34, 35 of the first and second projecting parts 30, 31 enables these projecting parts to be brought into alternative engagement.

The thus cold formed sheet material is then fed to a clenching device 42 where a plurality of pairs of co-operating rolls 43 clench the projecting elements together and also form a recess 44 where the projecting parts overlap.

If desired, the above described recess 44 may be formed during the roll forming stage in the roll former 40.

More particularly, the projecting element 34 of the first side 31 is bent through 900 so as to overlap the second side 33, whilst the second projecting elements 35 are bent through 900 so as to overlap the first side 31. As a consequence, a rigid joint connecting the adjacent edges of the tubular shape thus formed is effected.

In either case a recess may extend continuously along the member or a plurality of separate recesses may be provided to receive the projecting parts 34, 35 and there being un-recessed parts therebetween If it is desired to provide the structural member with a separately formed attachment component to provide the attachment portion of the member, the sheet section described hereinbefore is cut to the desired length for a body part as best shown in Figure 8. Figures 9-lla show some alternative forms of separate attachment component at 50. It will be seen that the attachment component shown in Figure 9 is of channel section and can be fixed in position by suitable fasteners engaged in the apertures 17 and the apertures 51, the apertures 52 being provided for attachment of the structural member in a desired application.

In Figure 10, two separate generally channel-shaped members are provided, again with fasteners being engaged with the apertures 17 and 51. In this case, only a single fastening aperture 52 is provided for connection of the structural member in use.

In Figures lia and lib alternative forms of attachment component are shown which are of a welded configuration. The same reference numerals have been used to refer to corresponding parts.

Of course, if desired, the configuration of the attachment component may be modified as desired and holes 17a shown in the transversely extending sides of the body part B may be used, if desired, alternatively or in addition, depending upon the configuration of the attachment component.

Referring now to Figures 12-15, an alternative embodiment is illustrated in which the body part B is formed integrally with an attachment portion 55 with an intermediate portion 56 being disposed therebetween.

As best shown in Figure 13 and Figure 15 first and second transverse sides 57, 58 which extend between upper and lower sides 59, 60 on opposite sides of the tubular shape are acted upon, at opposite ends of the member, by a pair of punches 61, 62 respectively to form transverse portions 57 58a of the sides 57, 58 with an inward depression so that the transverse portions S7L 58a are deformed inwardly to provide each transverse portion with an upper part 63 and a lower part 64. The upper and lower transverse parts 63, 66 are interconnected, by virtue of being integral therewith with each other, as shown at 65, and with upper and lower portions 59a, 60a as shown at 66, 67 respectively. The upper and lower portions 59a, 60a are displaced inwardly from their originally occupied positions as a result of the deformation above-described. They are then acted upon by further tools, 70, 71 as shown in Figure 14 so as to move them to the position shown in Figure 12 where the attachment portion 55 is flattened and the upper and lowers portions 59t, 60a and transverse parts 63, 64 are in a face-toface engagement. The tools 70, 71 have a transverse part 72 which acts upon the portions 59= 60a and an inclined part 73 which defines the shape and slope of the intermediate portion 56.

In a modification of the manufacturing method, the rotary punching unit may be omitted and the edge notching to produce the projecting parts may be performed either in the prepunching press 16 or by a suitable hydraulic or mechanical notching apparatus provided on the conveyor 19.

A further alternative is to provide off line notching of the edges of the coil by use of the apparatus shown in Figure 16 where a coil of sheet material 110 is uncoiled in a decoiler 111 and fed via a loop 112 through a notching press 113 where the sheet material is formed to the configuration described hereinbefore in connection with the rotary punching unit.

The notched sheet material is then fed via a further loop 114 to a recoiler 115 in conventional manner. The thus notched coil, 110' may then provide the coil 10 of the apparatus shown in Figure 1 but with the omission of the rotary punching unit 21.

Finally, in a further alternative illustrated in Figure 17, where the same reference numbers have been used to refer to corresponding parts, the body part B of the tubular member is made of two components. In this embodiment the two components are indicated at 200, 201 and are made in the manner described hereinbefore, except that the roll forming operation produces the components 200, 201 to an angle shape instead of a box shape. The two components 200, 201 are then brought together prior to being fed to the clenching device 42 which is differently configured and is conveniently provided off-line so that first and second projecting parts, 30, 32 are again caused to over-lie the second side 33 and the first side 31 respectively and, in addition, further similar first and second projecting parts 30,32 are provided, as illustrated at 202 whereby the components 200, 201 are securely joined together. This alternative manner of manufacture is particularly desirable where the structural member is of a relatively large size.

It may be used to provide a structural member with an integral attachment portion or an attachment portion provided as at least one separate component as described hereinbefore and in connection with the first embodiment.

If desired the sheet material may be roll formed to any desired configuration so long as adjacent edges are connected at a corner, as described hereinbefore. For example, the material may be cold rolled to form at least one rib or groove in its external surface.

As hereinbefore described, rotary punching and forming enable the structural members to be produced very economically.

The structural member may be provided in any desired application, for example, wind bracing, gable posts or corner posts in industrial buildings, door framing for industrial doors, gable rafters, head trim, compression trusses, stanchions, vaulted frames, eaves beams and cladding support beams. They may also be provided in portable accommodation units and used as lintels.

It should be appreciated that, by displacing portions of the member out of its original cross-section to positions adjacent to one another to provide the attachment portions, sufficient thickness of material can be provided for fastening means, such as bolts to co-operate directly with the attachment portions. Thus a structural member, according to this aspect of the invention, provides a satisfactory transfer of forces between the or each attachment portion and the rest of the member whilst enabling the member to produce economically. It will be appreciated that the embodiments described hereinbefore do not require access to be gained to the interior of a section. Structural members embodying the invention overcome the disadvantages discussed hereinbefore in connection with the structural members made previously from hot rolled members, in that they are made from material cut to length, without waste, and avoid the need for extensive welding operations followed by shot blasting and painting since the sections may be made from galvanised steel and the members are of lighter weight. In addition the members avoid the connecting difficulties previously encountered in the proposals for a cold formed member as described hereinbefore.

Although a rectangular tubular cross-section has been described herein so that the side and resultant projecting parts, or tabs, after clenching, are inclined at 90" the tubular cross-section may be of other polygonal shape such as triangular or hexagonal. The smaller the angle between the sides the less effective is the clenched connection and for this reason particularly a rectangular cross-section is preferred.

The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. An elongate structural member comprising an elongate body part of tubular shape of, polygonal cross-section, made of sheet metal which has been cold formed to provide said tubular shape with at least a pair of adjacent edges of the sheet metal being connected together, wherein said pair of adjacent edges are disposed at or adjacent a corner of the tubular shape at which first and second sides, terminating in said adjacent edges, converge to provide a salient angle therebetween and are joined together by a first projecting part of said first side which overlaps said second side and a second projecting part of said second side which overlaps said first side.

2. A member according to claim 1 wherein the elongate body part is a unitary member longitudinally bounded by said pairs of adjacent edges.

3. A member according to claim 1 wherein the body part comprises a compound member, comprising two or more components secured together, each component forming part of the overall cross-section of the body part.

4. A member according to claim 3 wherein one edge of said pair of edges is provided on one component, and the other edge of said pair of edges is provided on the other component.

5. A member according to claim 3 or claim 4 comprising at least one further pair of adjacent edges where the sheet metal is connected together and the or each pair of said adjacent edges being disposed at or adjacent a further comer of the tubular shape at which further first and second sides converge to provide a salient angle therebetween and a further first projecting part of said first further side overlaps said further second side and a further second projecting part of said further second side overlaps said further first side.

6. A member according to any one of the preceding claims wherein each first and second projecting part comprises a plurality of first and second projecting elements respectively.

7. A member according to claim 6 wherein first projecting element is disposed alternately relative to each second projecting element.

8. A member according to claim 6 or claim 7 wherein each first and second projecting element is of generally rectangular configuration comprising a pair of generally parallel sides projecting outwardly from adjacent inner edge parts and terminating in an outer edge parf which is generally perpendicular to each of said sides.

9. A member according to claim 8 wherein said sides, whilst being generally perpendicular to said inner and outer edge parts are inclined thereto to provide a taper whereby the projecting elements decrease in width towards the outer edge part.

10. A member according to any one of the preceding claims wherein the comer is a right-angle and each first projecting part is formed through substantially a rightangle.

11. A member according to any one of the preceding claims wherein the first and second projecting parts are disposed in a recessed portion of the side which the respective projecting part overlaps so that the external surface of the projecting parts lies substantially in the same plane as the external surface of the main part of the side which it overlaps.

12. A member according to any one of the preceding claims wherein the body part is provided with an attachment portion at each end.

13. A member according to claim 12 wherein the body part has upper and lower sides interconnected by first and second transverse sides extending normally to the respective upper and lower sides over the majority ofthe length of the body part, the body part having at least adjacent one end a flattened attachment portion so that in this portion the first and second transverse portions of the respective transverse sides are deformed so as to have two parts lying substantially parallel to and between upper and lower portions ofthe upper and lower sides.

14. A member according to claim 13 wherein the flattened portions lie substantially midway between the upper and lower sides.

15. A member according to any one of claims 12 to 14 wherein at least one attachment portion comprises portions of the elongate member displaced out of their original cross-section positions into positions adjacent to one another and adapted to co-operate with fastening means.

16. A member according to any one of claims 12 to 15 wherein the attachment portion comprises an upper portion parallel to an upper side of the body part, a lower portion parallel to a lower side of the body part, said upper and lower portions being displaced inwardly relative to their associated upper and lower sides and, disposed therebetween, at opposite sides thereof, first and second transverse portions, each comprising an upper part and a lower part disposed generally in face-to-face relationship with each other and with the respective upper and lower portions and the upper part being connected, at one side, to an outer edge ofthe upper portion and being connected, at an opposite side, to one edge ofthe lower part and the lower part being connected at its other edge to an outer edge of the lower portion.

17. A member according to claim 16 wherein said first and second transverse portions are provided as an integral part of the first and second transverse sides of the body portion which are progressively deformed to said face to-face relationship in a transition region disposed between said body part and said attachment portion.

18. A member according to claim 12 wherein at least one attachment portion comprises an attachment component formed separately from said body part and fastened thereto.

19 A member according to claim 18 wherein the attachment portion is of channel-shape, the limbs ofthe channel being disposed in side-by-side relationship with two opposed walls ofthe body part.

20. A member according to claim 18 or claim 18 wherein the attachment component is fastened to said body part by fasteners.

21. A member according to any one of the preceding claims wherein reinforcing means are provided to reinforce the walls of the body part.

22. An elongate structural member as hereinbefore described with reference to the accompanying drawings.

23. A method of providing an elongate structural member comprising a body part of tubular shape, of polygonal cross-section, comprising the steps of cold forming sheet metal to provide said tubular shape and connecting together at least a pair of adjacent edges of the sheet metal and providing a first projecting part of a first side and a second projecting part of a second side of said body part, performing said cold forming step so that said pair of adjacent edges are disposed at or are adjacent a comer of the tubular shape at which said first and second sides converge to provide a salient angle and forming said first projecting part to overlap said second side and said second projecting part to overlap said first side.

24. A method according to claim 23 wherein said first and second projecting parts are provided by a rotary punching unit comprising a pair of rotatable punching elements, one of which is provided with a plurality of recesses and the other of which is provided with a plurality of co-operating projecting punches whereby edge portions of the sheet are punched to provide said projecting portions between parts of the sheet which are punched out by the rotary punching unit.

25 A method according to claim 23 wherein the first and second projecting parts are made by a punching operation in a reciprocatory punching unit comprising a first die provided with a plurality of recesses and a second die provided with a plurality of cooperating projecting punches, said dies being reciprocal towards and away from each other so as to provide said projecting parts between portions of the strip which are punched therefrom by said punching unit.

26. A method according to claim 25 wherein the punching operation is repeated along the length of the strip.

27. A method according to any one of claims 23 to 26 wherein the first and second projecting parts are provided before the sheet metal is cold formed to said hollow shape.

28. A method according to any one of claims 23 to 25 wherein the sheet metal is formed to said hollow shape by roll forming.

29. A method according to any one of claims 23 to 28 wherein the sheet metal is fed to a pre-punch unit before being provided with the first and second projecting parts, or being roll formed, whereby desired openings may be provided in the sheet metal.

30. A method according to any one of claims 23 to 29 wherein the method comprises the further step of displacing attachment portions of the member out of their original cross-sectional positions into positions adjacent to one another.

31. A method according to claim 30 wherein means are provided for cooperation of said portions with fastening means.

32. A method according to any one of claims 23 to 31 wherein the body part has an upper side and a spaced lower side interconnected by first and second transverse sides perpendicular thereto and means are provided to displace said first and second transverse sides inwardly, at least at one end, to provide the or each attachment portion, with first and second transverse portions disposed between upper and lower transverse portions, the first and second transverse portions comprising respectively upper and lower transverse parts disposed in face-to-face flattened relationship.

33. A method according to claim 32 wherein the transverse portions are initially displaced partially inwardly to an intermediate position to reduce the spacing between said upper and lower portions and subsequently pressure is applied to said upper and lower portions to reduce their spacing further and cause the transverse portions that have said upper and lower parts to be brought into face-to-face relationship.

34. A method according to any one of claims 30 to 33 wherein die means are provided to define the inclination of the upper and lower sides in an intermediate region between the body part and the attachment portion.

35. A method of providing an elongate structural member substantially as hereinbefore described with reference to the accompanying drawings.

36. An elongate structural member when made by a method according to any one of claims 23 to 35.

37. Any novel feature or combination of features disclosed herein.